[Illustration: _Hair of an Egyptian woman. 5020 ± 290 years old._]
[Illustration: _Linen wrapping from the Dead Sea Scroll containing the
Book of Isaiah. 1917 ± 200 years old._]
[Illustration: _Peruvian rope. 2632 ± 200 years old._]
[Illustration: _Preglacial wood found in Ohio. More than 20,000 years
old._]
[Illustration: _Rope sandal found in an eastern Oregon cave. One of a
pair of 300 pairs found in this cave. 9035 ± 325 years old._]
Carbon-14 is by far the most widely used method of measuring geologic
time. It has become the mainstay of archeology and geology for studies
of events of the past 50,000 years or so, and also has wide applications
in climatology, ecology, and geography. It would be difficult to pick
out the most significant example of the use of this method, but one
important contribution has been in study of the early inhabitants of
North America. With the aid of ¹⁴C it has been possible to date human
living sites from many points in the western United States. The first
appearance of these sites, about 11,500 years ago, apparently coincided
with the time when a land bridge was open from Asia to America over what
is now the Bering Strait. An ice-free passage extended from this bridge
through present-day Alaska and western Canada to the United States. This
may have been the route taken by the first immigrants to America—a
population of mammoth-hunters, who made the characteristic flint
_Clovis_ arrow and spear points.
[Illustration: _A Clovis arrow point chipped from flint by the earliest
men on the American continent. The photograph is actual size._]
By about 11,000 years ago, these Clovis people had spread across the
area of the United States and into Mexico. It may have been they who
killed off the mammoths and then gradually assumed the characteristics
of the _Folsom_ culture. The Folsom people were bison-hunters, and long
were thought to have been the first population in America. It was with
the use of ¹⁴C that it finally was possible to place these two cultures
in proper sequence—the Clovis first—and to correlate them with major
natural changes, especially the advance and retreat of glaciers across
the continent.